DC motor starting circuit controlled by rheostat

As shown in the figure, when the power switch QS is turned on, the time relay 1KT operates and its normally closed contact is disconnected. Press the start button ST, the DC contactor 1KM operates, its normally closed contact disconnects the 1KT coil, the normally open contact 1KM connects the motor armature circuit, and is connected in series to all starting rheostat RP. The voltage generated by the armature current on RP drop, causing the time relay 2KT to operate, and its normally closed contact disconnects the 3KM coil circuit. After the delay, first the normally closed contact of the 1KT delayed closing is closed, and the 2KM is powered on to short-circuit part of the RP to speed up the armature. At the same time, the 2KT coil is also short-circuited by the normally open contact of 2KM. After a delay, the delayed closed normally closed contact of 2KT is closed, and 3KM is electrically activated, and its normally open contact also short-circuits the other part of RP. Then the motor enters the rated DC voltage operating state.